This invention relates to a process for preparing a poly(vinylbenzyl ether) of a polyphenol and a process for reducing the halide ion content of the prepared ether.
Poly(vinylbenzyl ethers) of polyphenols are thermoset resins disclosed in U.S. Pat. No. 4,116,936 (Steiner). They are prepared by initially dissolving a polyphenol and vinylbenzyl chloride in a solvent, e.g. acetone. The mixture is heated and a potassium hydroxide solution is added slowly. After the reaction of the mixture, the ether is first separated from precipitated potassium chloride by filtration or extraction and then separated from the remaining reaction product mixture by precipitation into methanol.
The Steiner process has four distinct disadvantages. First, the solvent employed to dissolve the polyphenol and the vinylbenzyl chloride also dissolves the prepared ether. The prepared ether must then be separated from the reaction product mixture, causing an increase in processing time and a reduction in yield. Second, the solvent reacts with the potassium hydroxide and forms undesirable byproducts that can be difficult to remove. Third, the residual chloride ion content of the prepared ether is at least 100 parts per million (ppm), typically greater than 500 ppm. The chloride ion content increases the dielectric constant and the dissipation factor of the cured resin, factors which adversely affect the performance of the resin for electronics applications. Fourth, polymer formed by the reaction of the vinyl groups with each other is difficult to remove and also adversely affects the performance of the resin.
In view of the deficiencies of the prior art, a process for preparing a poly(vinylbenzyl ether) of a polyphenol is needed which does not require a solvent that either reacts significantly with any of the reactants to form undesirable byproducts or dissolves the prepared ether. Also, a process is needed for preparing a poly(vinylbenzyl ether) of a polyphenol with a reduced halide ion content and a reduced vinyl polymer content.